Al2O3 Regions/Grains in ODS Steel PM2000 Irradiated With Fe Ions at 700 °C

Oxide dispersion strengthened (ODS) steel is one of the candidate structural materials for Generation-IV nuclear reactors. The microstructure of as-rolled PM2000 steel irradiated with 3.5 MeV Fe13+ ions at 700 °C to 0.75 dpa was studied using transmission electron microscopy in combination with the microstructure of the unirradiated steel. In difference to unirradiated steel, white blocky regions appeared in the irradiated steel and were identified to belong to Al2O3 oxide with a base-centered monoclinic crystal structure. The irradiation induced the formation of the Al2O3 regions in the steel. Segregation of alloy elements in the irradiated steel, characterized by Ti enrichment at the Al2O3/Fe interface, was observed. Three types of dispersed phases were found in the Al2O3 regions, respectively: Fe-rich M7C3 and Cr-rich M7C3 carbides with a simple orthorhombic lattice, and Y3Al5O12 oxide with an orthorhombic structure. Fe-rich M7C3 and Cr-rich M7C3 carbides were irradiation-induced precipitates. In order to better evaluate the Al2O3 layer on the surface of ODS steel under irradiation conditions, it is more reasonable to study the Al2O3 layer grown on the steel surface during irradiation.